1. Field of the Invention
This invention relates to a video tape recorder (VTR) and in particular, is directed to a VTR suitable for use with a so-called low frequency-converted signal recording and/or reproducing system in which a chrominance subcarrier signal is low frequency-converted, recorded on a recording tape together with a frequency modulated luminance signal and reproduced therefrom.
2. Description of the Prior Art
In an apparatus for recording and/or reproducing a low frequency-converted carrier signal in which a low frequency-converted carrier chrominance signal S.sub.C is recorded on a recording tape together with a frequency modulated luminance signal S.sub.Y, the deviation range of the frequency-modulated frequency is occasionally made different from that of the existing one in use.
FIG. 1A shows a frequency spectrum of an existing low frequency-converted color video signal S.sub.CV in a case where the deviation width of the frequency-modulated frequency is selected in a range from 3.8 MHz to 5.4 MHz and the low frequency-converted frequency fc is selected as, for example, 688 KHz (in the case of NTSC system), while FIG. 1B shows a frequency spectrum of a low frequency-converted color video signal S.sub.SP in a case where the deviation frequency is selected higher than the afore-said frequency by 1.0 MHz.
When the first and second color video signals S.sub.CV and S.sub.SP which are the same in frequency-modulated deviation width but different in deviation frequency and are recorded on the same tape T in the mixed state as, for example, shown in FIG. 2 are reproduced or when a video information is reproduced not from a tape on which only the first color video signal S.sub.CV is recorded but from a magnetic tape on which only the second color video signal S.sub.SP is recorded, the reproducing system of a VTR must selectively change over a circuit constant such as a cut-off frequency of a low-pass filter used in, for example, a frequency demodulator in accordance with the color video signals S.sub.CV and S.sub.SP to be reproduced.
For such case, it is considered to form the reproducing system of the VTR as shown in FIG. 3.
FIG. 3 illustrates a reproducing system 10 for only a luminance signal system. As shown in FIG. 3, a first or second color video signal S.sub.CV or S.sub.SP reproduced by a magnetic reproducing head H.sub.P from a magnetic tape T is supplied through a preamplified 2 to a frequency demodulator 3 in which a luminance signal Y.sub.CV or Y.sub.SP is demodulated, which then is fed to a second low-pass filter 4, in which the band of the luminance signal Y.sub.CV or Y.sub.SP is restricted by a predetermined amount.
For example, when the filter characteristic suitable for the first luminance signal Y.sub.CV is selected as shown by F1 n FIG. 4, the filter characteristic suitable for the second luminance signal Y.sub.SP is selected as shown by F2 which is extended as compared with F1 in high frequency region so that the filter characteristic of the second low-pass filter 4 is selected as F2.
A first low-pass filter 5 having a filter characteristic F1 is connected at the post stage of the second low-pass filter 4 and a switching circuit 6 is provided for selectively supplying the outputs from these low-pass filters 4 and 5 to an output terminal thereof. The switching circuit 6 is changed over such that only when the first luminance signal Y.sub.CV is demodulated, the output from the first low-pass filter 5 is delivered from the switching circuit 6.
To this end, the first or second luminance signal Y.sub.CV or Y.sub.SP thus demodulated is supplied to a synchronizing signal separating circuit 7 in which each of horizontal synchronizing signal P.sub.HC and P.sub.HS is respectively separated from the first and second luminance signal Y.sub.CV or Y.sub.SP to thereby form a gate pulse P.sub.G, by which the horizontal synchronizing pulse P.sub.HC or P.sub.HS of the first or second luminance signal Y.sub.CV or Y.sub.SP is gated. Reference numeral 8 designates a gate circuit therefor.
When the input and output characteristic of the frequency demodulator 3 is selected as shown by a straight line l in FIG. 5, the horizontal synchronizing pulses P.sub.HC and P.sub.HS of the frequency-demodulated first and second luminance signals Y.sub.CV and Y.sub.SP are different in DC level. This level difference is used to discriminate the first and second color video signals S.sub.CV and S.sub.SP from each other. To this end, the gate horizontal synchronizing pulses P.sub.HC and P.sub.HS from the gate circuit 8 are supplied to a level comparator 9 in which the DC levels thereof are respectively compared with a reference level so as to produce a compared output P.sub.C of "H" (high level) for, for example, the horizontal synchronizing pulse P.sub.HC and the compared output P.sub.C of "L" (low level) for the horizontal synchronizing pulse P.sub.HS.
The switching circuit 6 is controlled by the compared output pulse P.sub.C such that when the first color video signal S.sub.CV is reproduced, the output from the first low-pass filter 5 is always delivered therefrom while when the second color video signal S.sub.SP is reproduced, the output from the second low-pass filter 4 is always delivered therefrom.
When the gate pulse P.sub.G is formed from the demodulated first or second color video signal S.sub.CV or S.sub.SP, upon reproducing, if a dropout occurs, the horizontal synchronizing pulses P.sub.HC and P.sub.HS used for forming the gate pulse P.sub.G can not be synchronously separated positively. As a result, the low-pass filters 4 and 5 can not be changed over precisely.
Further, when a noise SN as shown in FIG. 6 enters the video signal, the synchronizing separating circuit 7 is mal-functioned by the noise SN so that also in this case, the low-pass filters 4 and 5 can not be changed over accurately.